My solution

// 1: Select the element with the ID 'about'. 
//    Store the element in the variable `about`.
const about = document.querySelector('#about');
about.style.border = "2px solid firebrick";

// 2: Select all the <h2> elements in the document.
//    Set the color of the <h2> elements to a different color.

const h2s = document.querySelectorAll('h2');

for(h2 of h2s) {
  h2.style.color = "orchid";
}


// 3: Select all elements with the class '.card'. 
//    Set their background color to the color of your choice.

const cards = document.querySelectorAll('.card');

for(card of cards){
  card.style.backgroundColor = "cyan";
}

// 4: Select only the first <ul> in the document.
//    Assign it to a variable named `ul`.

const ul = document.querySelector('ul');
ul.style.border = "2px solid indigo";

// 5: Select only the second element with the class '.container'.
//    Assign it to a variable named `container`.

const container = document.getElementsByClassName('container')[1];

container.style.backgroundColor = "royalblue";

// 6: Select all <a> elements that have a 'title' attribute. 
//    Set their color value to the color of your choice.

const anchorsWithTitle = document.querySelectorAll('a[title]');

for(a of anchorsWithTitle){
  a.style.color = 'orchid';
}