1. Prefix mess

    Browser vendors sometimes add prefixes to experimental or nonstandard CSS properties and JavaScript APIs, so developers can experiment with new ideas while — in theory — preventing their experiments from being relied upon and then breaking web developers' code during the standardization process.

    .my-class {
    -webkit-transition: left 400ms ease-out;
    /* older webkit */
    -webkit-transition: left 400ms ease-out;
    -moz-transition: left 400ms ease-out;
    -ms-transition: left 400ms ease-out;
    -o-transition: left 400ms ease-out;
    transition: left 400ms ease-out;
    }
    Check out what is going on here
  2. Link & the forgotten accessibility

    One of the most common mistakes: setting a color for a link, but not adding :hover, :focus and :active states.

    a {
    color: #ca0000;
    text-decoration: none;
    }

    /* And that is the end of link styling */
    Check out what is going on here
  3. z-index hell

    z-index is something that can measure one's frustration. The amount of digits represent the fact that the developer tried to position the div above the content, but failed miserably.

    .my-class {
    z-index: 122828282882;
    }
    Check out what is going on here