HTML-The HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript. It defines the meaning and structure of web.HTML are basically case-insensitive,but there are exception for entities such as class,id etc.
HTML Common Tags
META TAGS
Meta <meta> tags are pieces of information you use to tell the search engines and those viewing your site more about your page and the information it contains.The meta tags don't appear on the page itself, but only in the page's source code. Meta tags are essentially little content descriptors that help tell search engines what a web page is about.
TYPOGRAPHY
HEADING TAGS - This are used to separate headings and subheadings on a webpage <h1-h6> . They rank in order of importance, from H1 to H6.
PARAGRAPH - The <p> tag in HTML defines a paragraph.These have both opening and closing tag.
CONTAINERS
To make a container you have to use <div> tag,which is an empty tag by giving a width and height you can determine the size of the container.
LINKS
The <link> tag is used to define a link between a document and an external resource. The link tag is used to link to external style sheets. This element can appear multiple times but it goes only in the head section. The link element is empty, it contains attributes only.
<a> TAGS
The <a> tag (anchor tag) in HTML is used to create a hyperlink on the webpage.This hyperlink is used to link the webpage to other webpages.It's either used to provide an absolute reference or a relative reference as its “href” value.
LISTS
ORDERED LIST - The <ol> HTML element represents an ordered list of items — typically rendered as a numbered list.
UNORDERED LIST - An unordered list is a collection of related items that have no special order or sequence. This list is created by using HTML <ul> tag. Each item in the list is marked with a bullet.
NAV TAGS
The <nav> HTML element represents a section of a page whose purpose is to provide navigation links, either within the current document or to other documents. Common examples of navigation sections are menus, tables of contents, and indexes.
SECTION TAGS
The <section> HTML element represents a generic standalone section of a document, which doesn't have a more specific semantic element to represent it. Sections should always have a heading, with very few exceptions.
FOOTER TAGS
The <footer> HTML element represents a footer for its nearest sectioning content or sectioning root element. A <footer> typically contains information about the author of the section, copyright data or links to related documents.
CSS-CSS is the language we use to style an HTML document. CSS describes how HTML elements should be displayed.
CSS Commonly used properties
COLOR
The color property in CSS is used to set the color to text, the background of the webpage, and also to set the color of borders.
FONT SIZE
Font-size is the CSS property that controls the size of the font on a webpage. There are several different values you can use to define the font-size property.
BACKGROUND COLOR
The background-color property sets the background color of an element.The background of an element is the total size of the element, including padding and border (but not the margin).
BACKGROUND
The background property in CSS allows you to control the background of any element.You can add color, image, gradients etc to beautify the file.
HEIGHT & WIDTH
The height and width properties are used to set the height and width of an element. The height and width properties do not include padding, borders, or margins.
MARGIN
The margin property defines the space around an HTML element. It is possible to use negative values to overlap content.You can also set margin to a specified part.For ex-margin-top, margin-bottom, margin-right, margin-left.
PADDING
The CSS padding properties are used to generate space around an element's content, inside of any defined borders.Similarly, in margin you can specify a particular area to be padded.
BOX MODEL
The CSS Box Model is used to create a definition for the way the HTML elements are organized on the screen. This approach accounts for options such as margins, padding, borders, and all the properties that manipulate them.Each element can be thought of as having its own box.
BORDER
The border property in CSS is used to style the border of an element. This property is a combination of three other properties border-width, border-style, and border-color.
BORDER RADIUS
The border-radius CSS property rounds the corners of an element's outer border edge. You can set a single radius to make circular corners, or two radii to make elliptical corners.
HTML-The HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript. It defines the meaning and structure of web.HTML are basically case-insensitive,but there are exception for entities such as class,id etc. 
CSS-CSS is the language we use to style an HTML document. CSS describes how HTML elements should be displayed.